Thermodynamics of Magic Systems

When I was at a writer’s conference in Denver, I pitched to a science fiction and fantasy (SF/F) editor for a NY publisher. After expressing disappointment that I wasn’t pitching an SF manuscript, he brightened and said, “But I usually like Fantasy written by SF authors.”

“Because their magic systems make sense?” Being an avid reader of SF/F (and all sub-genres), I knew exactly what he meant.

He agreed.

Later I heard several writers at that same conference express why they liked to write fantasy (“It’s so easy, because you don’t have to do research,” “You can make everything up,” and “Readers don’t expect accuracy”). I decided I’d have to counter these misinformed ideas.

There are fundamental scientific laws and logic most readers understand intrinsically. If SF/F world-builders address these laws, the realism of their worlds will be enhanced and their readers won’t be getting that nagging feeling they’re reading a puffed-up idiotic Hollywood script. So, the first subject we’ll tackle is the laws of thermodynamics as they apply to magic systems.

First Law: Thou shalt not create energy from nothing.

Physical sciences and engineering disciplines all address this rule in different ways (okay, okay—they don’t use King James English in their textbooks, but then, their textbooks are boring). When this law was discovered, chemists went off to play with gas pressures in closed systems while engineers used it to drive a stake through the heart of the perpetual motion machine, an idea most readers intrinsically understand is dead.

This law is about conservation of energy, meaning that energy can change forms and transfer from material to material, but it must come from somewhere. It can go through many transformations but in the end, a closed system will have the same energy it had in the beginning. Heinlein put it succinctly in The Moon Is A Harsh Mistress: “There ain’t no such thing as a free lunch” (yet another concept most readers understand).

Basically, magic can be considered the application of energy. As a fantasy writer, please take time to figure out where the energy for your magic comes from. Before you grumble about this heinous limitation upon your creativity—it’s a world-building exercise where you’re in total control and your magic system will benefit from it, I promise. Just because the energy comes from somewhere doesn’t mean it has to be rare or limited. For instance, it could come from sunshine or starlight or the life force of plants, animals, the universe (“Feel the Force, Luke”), etc. It can come from generous gods or the ground one walks upon. If you do pick an essentially unlimited source, you’ll find this raises other questions, such as: Why isn’t everybody performing magic? And, if they are, what will be the ramifications upon society, economics, etc.?

To the contrary, your energy source could be incredibly constrained, having to be mined from the ground by imprisoned faeries during a blue moon in winter. Obviously, its scarcity will have ramifications. Hunt down and define those complications; you’ll discover more about your characters and world.

Consider, as well, how characters would channel/transform/wield this energy. What are the risks and the costs involved? If magic in your world is fueled by the internal energy in characters, then I would expect to see an incredible cost associated with a work requiring great power. After all, how much energy could be pulled from characters before they turn into dry husks–and before a reader says, “Come on now, this is a vapid Hollywood creation,” and throws it against the wall?

The second law of thermodynamics was discovered when trying to explain the direction of spontaneous change. Scientists observed that gas always expands to fill a vacuum, but never spontaneously contracts. Nature obviously abhors a vacuum, but why? Why do chemical reactions always proceed in one particular direction? Engineers also noted that heat (energy) never flows from a cooler to a hotter body. Spontaneous change is predictive and has a direction, but scientists wanted to know why. The answer: Systems change toward greater distribution of energy, toward greater “disorder,” which scientists called the entropy of a system. Entropy turned out to be measurable.

You’re probably thinking this entropy stuff can’t possibly be sensible to readers. Surprisingly, it’s quite intuitive when stated this way: Systems naturally change toward greater disorder, and it often takes more energy to apply or maintain order than disorder. We see examples of this in our everyday lives. It’s so much easier to drop your stuff on the floor in the family mudroom than put it away in those nicely labeled cubbyholes. Eventually someone (mom or dad) snaps and orders a family clean-up. Everyone finds it takes a good amount of energy to impose order upon that mudroom, while it seemed to naturally change or “decay” into disorder.

What does this mean to magic systems and your average reader? Let’s say you have a mage encase a city in a magical forcefield. No one can get in or out of that city. After this feat is performed, are you going to have the mage walk away with the guarantee this forcefield will be in effect forever? Only if you want your reader to dump your book, because we all sense that something of such high complexity and order requires energy to maintain it. This applies to even small abstract entities/spells like “wards,” as well. A fantasy I recently read had mages using wards like doorbells to sense when they had visitors and identify them. The author mentioned these wards needed continual maintenance—a careful detail that made her world more solid.

What if, instead, that mage reduced the city to dust? Would the reader believe the job is done and the mage can walk away? (Moral/ethical implications aside, of course.) Yes, the reader would consider the task completed and irreversible, but why is that? Because our world has engraved the instinct in us that no energy is required to maintain immense disorder. Furthermore, we understand the energy required to reorder that dust back into a city would be astronomical. The second law of thermodynamics is behind the maxim that “destruction is easier than creation.”

Entropic change also affects knowledge (Information Theory has the principle of degradation, where changes to information over time/transmission are irreversible). Everybody knows how the Greek Dark Ages and the Western European Dark Ages walloped advancement in those civilizations. From our own history, readers sense that a body of information requires continual energy to stay “ordered,” meaning relationships between data must be maintained or adjusted as knowledge increases. Copies must be made, distributed, and protected, whether by monks or computers.

In fantasies, having plot-critical magical lore established hundreds or thousands of years ago has almost become stock background. When information has to be transferred over many generations, when it must survive wars and natural disasters, the author should create inaccuracies and gaps. Otherwise, the credibility of the entire world is weakened. If your character is lucky enough to find good (never perfect) information, the author should provide hints on how it’s been preserved, whether through immortals with eidetic memory, fanatic quill-wielding clerks, multiple copies, special preservation methods, or survivable mediums.

Wrapping it up…

If your magic system fits within these first two laws, it will feel natural and solid to your readers. These simple premises are ingrained: we know energy comes from somewhere and we assume spontaneous change always moves toward disorder. We instinctually feel that the natural progression of time makes organized matter “decay” toward randomness. Use these instincts—based on natural laws of thermodynamics—to your benefit.